The physical uplink (UL) shared channel (PUSCH) power control has two components, an open loop component and a closed-loop component. Both the open and the closed loop components run consecutively, but asynchronously. The procedure is illustrated below, by way of example.
In a given UL subframe i (i=0 to any number), a PUSCH may be transmitted in the following manner: 1) on a dynamically assigned resource (by an UL grant on a physical downlink (DL) control channel (PDCCH)); 2) on a persistently assigned resource; or 3) not at all.
In a given DL subframe n, a power control command ΔPUSCH (n) for PUSCH power control may be provided in the following manner: 1) within an UL scheduling grant on PDCCH; 2) on a transmit power control (TPC) physical DL control channel (PDCCH), referred to as the TPC-PDCCHPUSCH; or 3) not at all.
If the PUSCH is transmitted in the subframe i, it is transmitted with the power PPUSCH (i). In the power control formula below, let KPUSCH=the delay in the PUSCH power control, i.e., a power control command provided in DL subframe n (n=0 to any number) will not impact the PUSCH transmit power in subframes prior to subframe n+KPUSCH.
Power control for PUSCH is described as follows. The power spectral density is controlled by a combination of open-loop and closed-loop techniques. The power spectral density is converted into transmit power by scaling according to the number of assigned resource blocks as indicated in the UL scheduling grant. The transmit power is limited by the maximum allowed power which depends on the wireless transmit/receive unit (WTRU) power class. There is a constant power value applied which is a combination of a cell-specific parameter and a WTRU-specific parameter. The open-loop component uses the downlink pathloss calculated in the WTRU from a reference symbol (RS) received power (RSRP) measurement and signaled RS transmit power. The pathloss in dB is scaled by a cell specific path loss compensation factor. The transmit power is adjusted by a modulation and coding scheme (MCS) variable signaled in each UL scheduling grant. Lastly, the closed-loop component is a specific correction value in dB included in every scheduling grant or jointly coded with other WTRU specific correction values on a TPC-PDCCHPUSCH.
The power control formula for PUSCH is defined below:PPUSCH(i)=min(Pmax,10 log10(M)+Po+α·PL+Δmcs+ƒ[ΔPUSCH(i−KPUSCH)])  Eq. (1)where:
the variable Pmax is the maximum allowed power (in dBm) that depends on the wireless transmit/receive unit (WTRU) power class;
the variable M is the number of assigned resource blocks as indicated in the UL scheduling grant;
the variable Po is a WTRU specific parameter (in dBm) with 1 dB resolution over a range of −126 dBm to 24 dBm;
the variable α is cell specific path loss compensation factor (can be set to one to allow full path loss compensation) that has eight values from 0.4 to 1 in steps of 0.1 with one of the possible values being zero;
the variable PL is the downlink pathloss calculated in the WTRU from a reference symbol received power (RSRP) measurement and signaled reference symbol (RS) transmit power;
the variable Δmcs is signaled by a RRC (Δmcs table entries can be set to zero) modulation and coding scheme (MCS) signaled in each UL scheduling grant;
ΔPUSCH is a WTRU specific correction value and is included in a UL scheduling grant or jointly coded with other WTRU specific correction values on a TPC-PDCCHPUSCH.
The WTRU attempts to detect a TPC-PDCCHPUSCH on every subframe except when in discontinuous reception (DRX) mode of operation. The power control formula may be applied to dynamically scheduled PUSCH or to persistently scheduled PUSCH.
For power control in dynamically scheduled PUSCH, the closed-loop correction value is a function ƒ[*] which represents either an accumulation or absolute value; the mode is signaled semi-statically via higher layers. When a new value of ΔPUSCH is received in the scheduling grant (SG),
For absolute controlƒ[ΔPUSCH(i−KPUSCH)]=ΔPUSCH(i−KPUSCH)
For accumulation control
      f    ⁡          [                        Δ          PUSCH                ⁡                  (                      i            -                          K              PUSCH                                )                    ]        =            ∑              m        =        0            i        ⁢          {                        Δ          PUSCH                ⁡                  (                      m            -                          K              PUSCH                                )                    }      
For power control in persistently scheduled PUSCH, the function ƒ[*] represents only accumulation. When a new value of ΔPUSCH is received in the TPC-PDCCHPUSCH,
      f    ⁡          [                        Δ          PUSCH                ⁡                  (                      i            -                          K              PUSCH                                )                    ]        =            ∑              m        =        0            i        ⁢          {                        Δ          PUSCH                ⁡                  (                      m            -                          K              PUSCH                                )                    }      
Power control for dynamically scheduled and persistently scheduled PUSCH, respectively, is described in the 3rd Generation Partnership Project (3GPP) specification. But, when both PUSCH are simultaneously scheduled as active, there is no solution on how to power control the two PUSCH together. A solution that controls the power of both the PUSCHs together is highly desirable.